This event corresponds to when attachments are saved to the messaging store. The BeforeAttachmentSave event occurs just before an attachment is saved when an item is saved. If a user edits an attachment and then saves those changes, the BeforeAttachmentSave event will not occur at that time; instead it will occur when the item itself is later saved. It also does not occur when the attachment is saved on the hard disk using the SaveAsFile method.

In VBScript, if you set the return value of this function to False, the save operation is cancelled and the attachment is not changed.